Treatment of sugar juice

ABSTRACT

A process for treating impure cane-derived sugar juice comprises subjecting, in a clarification stage, the juice to microfiltration/ultrafiltration to decrease the levels of suspended solids, organic non-sugar impurities and/or color therein. The resultant clarified sugar juice is sequentially passed through an ion exchange stage by bringing the juice into contact with a strong acid cation ion exchange resin in the hydrogen form, and thereafter into contact with an anion ion exchange resin in the hydroxide form. A purified sugar solution is withdrawn from the ion exchange stage, and concentrated to produce a syrup. The syrup is subjected to primary crystallization in a primary crystallization stage, to produce refined white sugar and primary mother liquor. The primary mother liquor is subjected to secondary crystallization in a secondary crystallization stage, to produce impure crystallized sugar and white strap molasses.

This application is a nationalization of and claims priority under PCTApplication No. PCT/IB00/00387 that was filed on Mar. 31, 2000. Thisapplication was published, in accordance with PCT Article 21(2), in theEnglish language as WO 00/60128 on Oct. 12, 2000. PCT Application No.PCT/IB00/00387 claimed priority under South African Patent ApplicationSerial No. 99/2568 that was filed on Jul. 4, 1999.

THIS INVENTION relates to the treatment of sugar juice. It relates inparticular to a process for treating impure cane-derived sugar juice,typically raw juice which has been subjected to conventionalpreclarification by heating, liming and settling.

According to the invention, there is provided a process for treatingimpure cane-derived sugar juice, which process comprises

subjecting, in a clarification stage, impure cane-derived sugar juice tomicrofiltration/ultrafiltration to decrease the levels of suspendedsolids, organic non-sugar impurities and/or colour therein;

sequentially passing the resultant clarified sugar juice through atleast one ion exchange stage by bringing the clarified sugar juice intocontact with a strong acid cation ion exchange resin in the hydrogenform, and thereafter into contact with an anion ion exchange resin inthe hydroxide form;

withdrawing a purified sugar solution from the ion exchange stage;

concentrating the purified sugar solution, to produce a syrup;

subjecting the syrup to primary crystallization in at least one primarycrystallization stage, to produce refined white sugar and primary motherliquor or molasses;

subjecting the primary mother liquor to secondary crystallization in atleast one secondary crystallization stage, to produce impurecrystallized sugar and secondary mother liquor or white strap molasses.

The impure cane-derived sugar juice typically is that obtained bypreparing sugarcane stalks, eg disintegrating or breaking up the stalks;removing sugar juice from the prepared stalks by diffusion and/ormilling, using imbibition water, thereby to obtain mixed juice; heatingand liming the mixed juice; and subjecting it to primary clarification,to obtain clear juice, ie to obtain the impure cane-derived sugar juicewhich constitutes the feedstock to the process of the invention.Instead, however, the clear juice or impure cane-derived sugar juicewhich is used as feedstock can be that obtained by any other suitablepreparation process.

The impure cane-derived juice is typically at an elevated temperature,eg a temperature above 90° C. Thus, the microfiltration/ultrafiltrationwill also be effected at elevated temperature; however, since ionexchange normally takes place at a lower temperature, eg at atemperature below 60° C., such as at about 10° C., the juice willnormally be cooled before ion exchange.

The impure sugar juice as obtained from sugar cane stalks ashereinbefore described, has a low sugar or sucrose concentration,typically less than 15% (m/m), for example in the order of 10% to 15%(m/m). This low concentration impure sugar juice is suitable as afeedstock for the process of the present invention; however, it isbelieved that it will be advantageous to use a higher concentrationimpure sugar juice as feedstock, eg to reduce the cost of the capitalequipment required to treat the same amount of sugar or sucrose. Thus,the process may include concentrating, eg by means of evaporation, theimpure sugar juice before it enters the clarification stage. It may beconcentrated to a sugar or sucrose concentration of at least 20% (m/m),preferably from 20% to 40% (m/m), typically about 25% (m/m).

The impure cane-derived sugar juice will thus normally, duringpreparation thereof, have been subjected to initial or primaryclarification; the treatment in the clarification stage of the processof the invention thus constitutes secondary clarification of the sugarjuice. In the secondary clarification stage, sufficient suspendedsolids, organic non-sugar impurities and colour are removed to renderthe sugar amenable to subsequent treatment in the ion exchange stage.During the secondary clarification, the sugar juice may be passedthrough a membrane in the size range 15000 Dalton to 300000 Dalton or200 Angstrom to 0,2 micron. The Applicant has found thatmicrofiltration/ultrafiltration prior to ion exchange is important inorder to inhibit rapid fouling of the ion exchange resins, and to ensurethat the refined white sugar product meets the required turbidityspecifications.

In the ion exchange stage, de-ashing or demineralization and furthercolour removal takes place. The contacting of the clarified sugar juicewith resins is effected in such a manner that inversion, ie breakdown ofsucrose to glucose and fructose is kept as low as possible, and resinuse is optimized.

In certain circumstances, strong acid cation resins can catalyze theinversion reaction of sucrose. To inhibit sucrose inversion in suchcases, the ion exchange, or a portion of the ion exchange, can beeffected at sugar juice temperatures below 30° C. The process may thusinclude, when necessary, reducing the impure sugar juice temperature tobelow 30° C., ahead of or during its passage through the ion exchangestage. For example, the sugar juice temperature can be reduced to about10° C., eg by using a refrigeration plant, to ensure minimal sucroseinversion.

The ion exchange stage may be provided by a simulated moving bedarrangement or system, eg by a continuous fluid-solid contactingapparatus such as that described in U.S. Pat. No. 5,676,826; by aseparation train system such as that described in U.S. Pat. No.5,122,275; or the like.

The process may include subjecting the clarified sugar juice to a firstpass through the ion exchange stage, to obtain a partially purifiedsugar solution, and thereafter subjecting the partially purified sugarsolution to at least one further pass through the ion exchange stage, toobtain the purified sugar solution.

The process includes regenerating the resins from time to time, asrequired. Thus, the strong acid cation resin may be regenerated bycontacting it with a strong acid, such as hydrochloric acid or nitricacid, with an acid stream rich in potassium salts thereby beingobtained. This component is suitable for use as a fertilizer feedstock.The anion resin may be regenerated by contacting it with a strong orweak base such as sodium hydroxide, potassium hydroxide, ammoniumhydroxide, or a combination of sodium or potassium hydroxide andammonium hydroxide, with an alkaline stream which is rich in nitrogenbeing obtained. This component is also suitable for use as a fertilizerfeedstock.

As indicated hereinbefore, de-ashing or demineralization (cations andanions) and colour removal are effected simultaneously in the ionexchange stage. However, the Applicant has found that it is not alwaysthe most efficient route to remove all colour during passage of thesugar juice through the ion exchange stage. Some colour may thus, ifdesired, be removed in the ion exchange stage, with the remaining colourthen being removed by further treatment of the sugar juice.

Thus, in one embodiment of the invention, the process may includesubjecting the purified sugar solution from the ion exchange stage, orthe partially purified sugar solution of the ion exchange stage, tofurther decolourizing in a decolourizing stage.

The decolourizing stage may comprise an anion resin, in particular ananion resin in hydroxide or chloride form; an absorption resin;activated carbon; or another absorption medium.

When the decolourizing stage includes an anion resin in the chlorideform, the partially purified sugar solution, after the first passthereof through the ion exchange stage, may be brought into contact withthe anion resin in the chloride form in the further ion exchange stage,and thereafter subjected to a second pass through the ion exchangestage.

When the decolourizing stage includes an anion resin in the hydroxideform, an absorption resin, activated carbon, or another absorptionmedium, the purified sugar solution from the ion exchange stage may bebrought into contact with the anion resin, the absorption resin, theactivated carbon or the other absorption medium.

The concentration of the purified sugar solution into the syrup may beeffected by means of evaporation. The resultant syrup may have a sucroseor sugar concentration of about 65% (m/m).

The primary crystallization may be effected in a plurality of sequentialprimary stages or boilings. The secondary crystallization may also beeffected in a plurality of sequential primary stages or boilings. Thepurge or mother liquor from the primary crystallization is thusexhausted further by the secondary crystallization to recover the impuresugar crystals. The impure crystallized sugar from all the secondarycrystallization stages or boilings may be remelted or redissolved, andrecycled to the syrup ahead of the primary crystallization stages. Thisrecycle is typically less than 20% of the total feed to the primarycrystallization stages. The purge or mother liquor from the secondary orexhaustion crystallization stages is thus defined as the white strapmolasses.

In another embodiment of the invention, the process may includesubjecting the syrup, prior to the primary crystallization, todecolourizing crystallization in a decolourizing crystallization stage,to produce high colour white sugar and tertiary molasses; remelting orredissolving the high colour white sugar to produce a remelted sugarsolution which is then subjected to the primary crystallization in theprimary crystallization stages; returning the primary mother liquor ormolasses produced in the primary crystallization stages to thedecolourizing crystallization stage; subjecting the tertiary molassesfrom the decolourizing crystallization stage to mill crystallization ina mill crystallization stage to produce the white strap molasses andimpure crystallized low colour sugar; and returning the impurecrystallized low colour sugar to the decolourizing crystallizationstage, with the decolouring crystallization and the mill crystallizationconstituting the secondary crystallization.

The white strap molasses is a low ash material suitable for varioususes, eg for fermentation, for the manufacture of high purityby-products, can be subjected to chromatographic separation for recoveryof sucrose, or can be used as a liquid sugar source. Thus, the whitestrap molasses is a secondary high value product. The white strapmolasses has, without further processing thereof, the following typicalproperties:

sucrose content of less than 40% on a dry solids basis;

sugar (sucrose, glucose and fructose) content of more than 75% on a drysolids basis, with the sucrose fraction depending on the ion-exchangestages;

ash (inorganic material) content of less then 2,0%;

organic non-sugars of less than 24%.

The invention extends also to the products obtained from the process ofthe invention, ie a potassium-rich acid stream or component, anitrogen-rich alkaline stream or component, white strap molasses, andrefined sugar, when produced by the process of the invention.

The Applicant has unexpectedly found that by subjecting impurecane-derived sugar juice to microfiltration/ultrafiltration andsubsequent ion exchange in accordance with the invention, removal ofsubstantially all the colour and turbidity which is present in theimpure cane-derived sugar juice is achieved. A purified sugar solutionsuitable for the direct production of white or refined sugar without anypre-crystallization or raw sugar house treatment thereof being required,is thereby obtained.

By contacting the clarified sugar juice with a strong acid cationexchange resin in the hydrogen form followed by an anion exchange resinin the hydroxide form, substantially all inorganic ions are removed;however, it was also unexpectedly found that in excess of 60% of theorganic non-sugars present in the sugar juice are also thereby removed.This thus means that in excess of 70% of the molasses non-sugarcomponents are removed by the ion exchange, which leads to higheroverall recovery of sucrose if sucrose inversion is minimized, as hereindescribed.

To minimize inversion of sucrose to glucose and fructose, the ionexchange is, as hereinbefore described, preferably effected in asimulated moving bed and at a low temperature. The simulated moving bedallows the acid released to be neutralized as the juice passes throughthe ion exchange bed, and also reduces the residence time. It was thussurprisingly found that by subjecting the sugar juice to ion exchange ina simulated moving bed, having at least one pass, at about 50° C., or atan even lower temperature, eg at about 10° C., in certain cases, theinversion is reduced to less than 1%.

To obtain both low inversion and sufficient colour and non-sugarimpurity removal is critical in order to achieve an economically viableprocess.

The invention will now be described by way of example with reference tothe accompanying drawings.

In the drawings,

FIG. 1 is a flow diagram of an impure cane-derived sugar juicepreparation process, as well as a process according to one aspect of theinvention for treating the resultant impure cane-derived sugar juice;and

FIGS. 2 and 3 are similar flow diagrams of impure cane-derived sugarjuice preparation processes, as well as processes according to secondand third aspects of the invention, respectively, for treating theresultant impure cane-derived sugar juice.

In FIGS. 1, 2 and 3, similar stages and flow lines are indicated withthe same reference numerals.

Referring to FIG. 1, reference numeral 10 generally indicates a processfor producing impure cane-derived sugar juice.

The process 10 includes a cane stalk preparation stage 12, with a sugarcane stalk feed line 14 leading into the stage 12.

A disintegrated stalk transfer line 16 leads from the stage 12 to adiffuser stage 18, with an imbibition water feed line 20 also leadinginto the stage 18. A fibrous residue or bagasse withdrawal line 22 leadsfrom the stage 18.

A mixed juice flow line 24 leads from the stage 18 to a primaryclarification stage 26, with a clear juice flow line 28 leading from thestage 26.

Reference numeral 30 generally indicates a process according to a firstaspect of the invention, for treating impure cane-derived sugar juice orclear juice from the process 10.

The process 30 includes a secondary clarification stage 32, with theclear juice flow line 28 leading into the stage 32. A recycle line 34leads from the stage 32 back to the primary clarification stage 26 or tothe diffuser stage 18 (not shown) or to a separate clarification stage(not shown).

A clarified sugar juice transfer line 36 leads from the stage 32 to asimulated moving bed ion exchange stage or system 40. The stage orsystem 40 comprises a continuous fluid-solid contacting apparatus, suchas that taught in U.S. Pat. No. 5,676,826, and which simulates a movingbed ion exchange arrangement in which the clarified sugar juice passessequentially through one or multiple ion exchange passes. The or eachion exchange pass comprises a strong acid cation ion exchange resin inthe hydrogen form, followed by an anion ion exchange resin in thehydroxide form.

A strong acid feed line 42 leads into the stage or system 40, with apotassium-rich acid withdrawal line 44 leading from the system 40. Abase feed line 46, for feeding a strong or weak base such as sodiumhydroxide, potassium hydroxide and/or ammonium hydroxide, also leadsinto the stage or system 40, while a nitrogen-rich alkaline streamwithdrawal line 48 leads from the system 40.

A purified sugar solution withdrawal line 50 leads from the system 40 toan evaporation stage 52, with a syrup transfer line 54 leading from thestage 52 to a redissolution and storage stage 56. A line 58 leads fromthe stage 56 to a primary or refining crystallization stage 60. Atransfer line 62 leads from the refining crystallization stage 60 to asecondary or recovery crystallization stage 64. A recycle line 66 leadsfrom the stage 64 back to the stage 56.

A refined white sugar withdrawal line 68 leads from the stage 60, whilea white strap molasses withdrawal line 70 leads from the stage 64.

In use, cane stalks enter the cane stalk preparation stage 12 along theline 14. In the stage 12, they are disintegrated and broken up, ieprepared for further processing. The disintegrated stalks pass, alongthe line 16, into the diffuser stage 18, where cane juice is removedtherefrom by means of imbibition water which enters the stage 18 alongthe line 20. Fibrous residue or bagasse is withdrawn along the line 22,and can be used as a fuel.

Mixed juice from the stage 18 is heated and limed (not shown), and thenpasses into the primary clarification stage 26, typically at atemperature above 95° C. In the primary clarification stage 26, whichtypically comprises a gravity settler, mud settles from clear juice, isremoved and filtered in filters (not shown) or returned to the diffuserstage 18. Where filters are used, the filtrate from the filters isreturned to ahead of the primary clarification stage 26, while thefilter cake is discarded.

The overflow from the clarification stage 26, ie clear juice or impurecane-derived sugar juice, passes along the flow line 28 to the secondaryclarification stage 32 where it is subjected tomicrofiltration/ultrafiltration by passing it through a membrane in therange 15000 Dalton to 300000 Dalton or 200 Angstrom to 0,2 micron,thereby to remove suspended solids, organic non-sugar impurities andsome colour. Clarified sugar juice is thus obtained in the stage 32. Theconcentrate or retentate from the secondary clarification stage 32 isrecycled, along the flow line 34, to the primary clarification stage 26or to the diffuser stage 18 to recover the sugar from the secondaryclarification or filtration concentrate and to remove the impuritiesretained through further clarification. The bulk of the clarified sugarjuice passes, after being cooled down to 10° C., along the flow line 36to the simulated moving bed ion exchange system 40 where it passessequentially through one or more ion exchange passes.

The strong acid cation exchange resin is regenerated by contacting itwith hydrochloric acid or nitric acid entering along the flow line 42,with a potassium-rich acid stream being withdrawn along the flow line44. Simultaneously, the anion ion exchange resin is regenerated by meansof a strong or weak base such as sodium hydroxide, potassium hydroxide,ammonium hydroxide, or a mixture of two or more thereof, which entersalong the flow line 46, with a nitrogen-rich alkaline stream beingwithdrawn along the flow line 48. The streams that are withdrawn alongthe flow lines 44, 48 are suitable for use as fertilizer feedstocks.

Purified sugar solution passes from the stage 40 along the flow line 50to the evaporator 52 where it is evaporated into a syrup. The syruppasses along the flow line 54 to the stage 56 where it joins impurecrystallized sugar which is returned via line 66 from the recoverycrystallization stage 64, which sugar is redissolved or remelted. Thecombination syrup and remelt stream passes along the flow line 58 to therefining crystallization stage 60 where it is subjected to primary orrefining crystallization in known fashion, with crystalline refinedwhite sugar being separated from the resultant primary mother liquor,and being withdrawn along the flow line 68.

The primary mother liquor passes from the stage 60 along the flow line62 to the recovery crystallization stage 64 where it is typicallysubjected to from two up to four boilings for secondary or recoverycrystallization thereof, with recovered impure crystallized sugar beingrecycled to the stage 56. White strap molasses is withdrawn along theflow line 70.

The white strap molasses 70, as hereinbefore described, typically has asucrose purity less than 40%; a sugars content (sucrose, glucose andfructose) of more than 75%; an ash content of less than 2.0% and anorganic non-sugar content of less than 24%.

The process 30 was simulated on pilot plant scale in the followingnon-limiting example:

EXAMPLE 1

A primary clarified sugar juice with the characteristics shown in thesecond row of Table 1 was generated from a sugar cane extraction plant.After secondary clarification by microfiltration/ultrafiltration (15000D ceramic membrane) of the juice, the solution had the analysis shown inTable 1 (row 3). The sugar solution was now passed through two ISEP(L-100B) (trademark) units obtainable from Advanced SeparationTechnology Inc of 5315 Great Oak Drive, Lakeland, Fla. 33815, USA. Theseunits are simulated moving bed strong acid cation/anion ion exchangeresin systems. The cation resin used was Amberlite IRA 252 RF(trademark) H styrenic macroporous strong acid resin. The anion resinused was Amberlite IRA 958 (trademark) Cl (but running as OH) acrylicmacroreticular strong base resin. Both these resins were supplied byRohm & Haas, 5000 Richmond Street, Philadelphia, Pa. 19137, USA. Thecation resin was regenerated with hydrochloric acid, while the anionresin was regenerated with caustic soda solution. The units wereconfigured so as to minimize residence time of the juice in contact witheither the anion or cation resins. The deionized solutioncharacteristics are shown in Table 1. The deionized juice wasconcentrated, crystallized, and centrifuged to yield a white strapmolasses and a refined sugar. The final sugar produced met thespecification as shown in Table 2.

TABLE 1 Total dissolved Turbidity Colour Ash Treatment solids (Brix)ICUMSA ICUMSA (% m/m) Primary Clarified Juice 12 9000 22000 .43Secondary Clarified 12 500 15000 .43 Juice Deionized Juice 10 4 135 <.01White Strap Molasses 84 <500 <5000 <1

TABLE 2 Analysis Pol Greater than 99.9% Ash Less than 0.015% Colour(ICUMSA) Less than 40 Invert Sugars Less than 0.1%

Table 3 illustrates the impact of ion-exchange passes and residence timeon inversion. For the ion exchange, the sugar stream temperature is inthe range of 40° C. to 75° C., and the fluid residence time in the rangeof 1 to 15 minutes.

TABLE 3 Feed Solution Sugar Temp- Solu- Residence Ash Sucrose StreamPasses erature tion Time Removal Inversion Clear 3 30° C. 12 10 min >98%1.0% Juice (three) (average) brix (average) (average)

Table 4 illustrates the removal of impurities compared to black strapmolasses.

The process of the invention eliminates the production of non-sugarimpurities of the conventional raw sugar factory, which adds about 8%non-sugar impurities compared to the feed non-sugar impurities.

TABLE 4 Removal of Removal of non-sugar non-sugar impurities via Name ofPurge impurities via Crystallization Technology (Molasses) Ion-ExchangePurge (Molasses) Conventional Raw Black Strap  0% of feed 104% of feedSugar Recovery Molasses The process of the White Strap 71% of feed  29%of feed invention Molasses

Referring to FIG. 2, reference numeral 100 generally indicates a processaccording to a second aspect of the invention, for treating impurecane-derived sugar juice or clear juice from the process 10.

The process 100 is similar to the process 30. However, the process 100includes an evaporation stage 102 between the primary clarificationstage 26 and the secondary clarification stage 32. The clear juice flowline 28 thus leads into the stage 102 rather than into the stage 32. Inthe evaporation stage 102, the clear or impure cane-derived sugar juiceis concentrated, by means of evaporation, from a sugar or sucroseconcentration of 10% to 12% (m/m) to about 25% (m/m), with theconcentrated clear juice passing to the secondary clarification stage 32along a flow line 104.

The process 100 also includes an additional decolourizing stage 106,downstream of the ion exchange system or stage 40, with the flow line 50leading into the stage 106, and a line 108 leading from the stage 106 tothe evaporation stage 52. The concentrated clarified sugar juicetypically passes through two ion exchange passes in the ion exchangestage 40, before passing to the decolourizing stage 106 where it iscontacted with an anion resin in the hydroxide or chloride form, anabsorption resin, activated carbon, or another absorption medium. In thedecolourizing stage 106 the residual or remaining colour is removed,with only some of the colour thus having been removed in the stage 40.

The process 100 was simulated on pilot plant scale in the followingnon-limiting example.

EXAMPLE 2

A primary clarified sugar juice with the characteristics shown in thesecond row of Table 5 was generated from a sugar cane extraction plant.After secondary clarification by microfiltration/ultrafiltration (500Angstrom ceramic membrane) of the juice, the solution had the analysisshown in Table 5 (row 3). The sugar solution was now passed through twoISEP (L-100B) and one ISEP (L100C) (trademark) units obtainable fromAdvanced Separation Technology Inc of 5315 Great Oak Drive, Lakeland,Fla. 33815, USA. These units are simulated moving bed strong acidcation/anion ion exchange resin systems. The cation resin used wasAmberlite IRA 252 RF (trademark) H styrenic macroporous strong acidresin. The anion resin used was Amberlite IRA 92 (trademark) (butrunning as OH) styrenic macroporous weak base resin. The decolourizingresin used was Amberlite IRA 958 (trademark) Cl (running as either OH orCl) acrylic macroreticular strong base resin. All these resins weresupplied by Rohm & Haas, 5000 Richmond Street, Philadelphia, Pa. 19137,USA. The cation resin was regenerated with hydrochloric acid, while theanion resin was regenerated with caustic soda solution. Thedecolourizing resin was regenerated with brine or caustic soda solution.The units were configured so as to minimize residence time of the juicein contact with either the anion or cation resins. The deionizedsolution characteristics are shown in Table 5. The deionized juice wasconcentrated, crystallized, and centrifuged to yield a white strapmolasses and a refined sugar. The final sugar produced met thespecification shown in Table 6.

TABLE 5 Total dissolved Turbidity Colour Ash Treatment solids (Brix)ICUMSA ICUMSA (% m/m) Primary Clarified Juice 13 4140 16940 .48Secondary Clarified 13 <500 16000 .48 Juice Deionized Juice 13 <400<6000 <.025 Decolourized Juice 13 <200 <300 <.025

TABLE 6 Analysis Pol Greater than 99.7% Ash Less than 0.005% Colour(ICUMSA) Less than 40 Invert Sugars Less than 0.04%

Referring to FIG. 3, reference numeral 200 generally indicates a processaccording to a third aspect of the invention, for treating impurecane-derived sugar juice or clear juice from the process 10.

The process 200 is similar to the processes 30, 100 in certain respects.For example, it includes the evaporation stage 102 of the process 100,and is similar otherwise to the process 30, up to the evaporation stage52.

The flow line 54 from the evaporation stage 52, in the process 200,leads to a decolourizing crystallization stage 202, where the syrup istypically subjected to one boiling, with low colour sugar and tertiarymolasses being produced.

The low colour sugar passes along a flow line 204 to a remelt orredissolution stage 212, with the redissolved sugar syrup, at a sugarconcentration of about 65% (m/m), passing along the flow line 58 to therefining crystallization stage 60, where it is typically subjected tofour boilings.

The flow line 62 from the stage 60 leads back to the dissolution stage56 and then to the stage 202.

The tertiary molasses produced in the stage 202 pass along a flow line206 to a mill crystallization stage 208, where it is typically subjectedto three boilings, with white strap molasses and impure crystallizedsugar being produced. The white strap molasses is withdrawn along theflow line 70, which thus leads from the stage 208, while the impuresugar is returned to the stage 202 along a flow line 210.

The mill crystallization stage 208 may typically comprise three boilingsor stages (not shown), with the impure sugar from the second and thirdstages being recycled, with remelting, to the first stage; with themolasses passing sequentially from the first to the second and then tothe third stage where it is withdrawn along the flow line 70, and withthe impure sugar from the first stage then passing along the recycleline 210, with remelting, back to the stage 202.

The process of the invention enables refined sugar to be produced in araw sugar factory or mill without the need for a standard cane sugarrefinery plant, by using microfiltration/ultrafiltration clarificationand ion exchange de-ashing and decolourizing.

In the process of the invention, white sugar can thus be produceddirectly from cane-derived sugar juice, at an increased recoverycompared to a standard cane raw sugar mill. The increased recovery is inthe range of 2% to 9% additional sucrose recovery at white sugarquality.

A low colour, low ash, high purity molasses, ie the white strapmolasses, is also obtained from the process according to the invention,together with potassium fertilizer and ammonium-based fertilizercomponents.

The Applicants have thus surprisingly found that with the process of thepresent invention, the production of crystalline sugar can be maximizedwhile minimizing the formation of liquid sugar, ie minimizing inversion.

It is believed that by using the cation exchange resin followed by theanion exchange resin, particularly good results are achieved. Forexample, a mixed cation/anion resin bed would present problems, eg itwould be difficult to regenerate economically, and is avoided in thepresent process. The process of the invention is thus characterizedthereby that it avoids the use of a mixed bed ion exchange resin.

In the process of the present invention, the problem of excessiveinversion is overcome, or at least reduced, by use of the ion exchangestage containing the cation and anion resins which the sugar juicecontacts sequentially, and in particular the use of a simulated movingbed ion exchange stage, coupled with temperature control during the ionexchange.

Another important feature of the present invention is the provision, inone version of the invention, of a separate decolourization stage forfinal colour removal in addition to the ion exchange stage, which isthen used primarily for demineralization or ash removal. This permitsready optimization of both the demineralization and the decolourizationof the sugar juice, and reduces the risk of inversion during cationexchange in the ion exchange stage.

The Applicants have also unexpectedly found that the process of thepresent invention, which embodies microfiltration/ultrafiltration, aswell as demineralization and at least some decolourization of the juiceprior to evaporation thereof into a syrup and crystallization intosugar, is both technically and economically feasible. In particular, itwas surprisingly found that the process of the present inventionsimultaneously fulfills the following requirements:

it directly produces refined sugar which meets universal specificationsfor colour, turbidity and ash, ie the process removes colour and ash;

it produces a high quality liquid sugar, ie the white strap molasses;

there is low inversion during processing, ie minimal sugar loss; and

there is efficiency of chemical usage.

The Applicants have further unexpectedly found that features such asusing the simulated moving bed, and separating the final colour removalfrom the demineralization, make the process more economically viable.The separation of the final colour removal from the demineralization wasfound to be necessary in some cases because the kinetics of theseoperations are not the same and furthermore the ash and colour levelsare not in proportion to one another. The Applicants thus found completede-ashing and decolourizing at high chemical efficiency can often not beachieved without separating the demineralization from the colour removaloperation.

It is also believed that the approach, in the process of this invention,of removing substantially all impurities from the sucrose solution, iefrom the sugar juice, by means of ultrafiltration/microfiltration andsubsequent ion exchange prior to crystallization, rather than usingcrystallization itself for purification of the sugar, is unique.

It is further believed that the ability of the process of the inventionto produce, in an economically feasible fashion, two useful sugarstreams, namely the refined white crystallized sugar and the white strapmolasses, is unique and unexpected.

What is claimed is:
 1. A process for treating impure cane derived sugarjuice, which process comprises subjecting, in a clarification stage,impure cane derived sugar juice to microfiltration/ultrafiltration todecrease the levels of suspended solids, organic non sugar impuritiesand/or colour therein; sequentially passing the resultant clarifiedsugar juice through at least one ion exchange stage by bringing theclarified sugar juice into contact with a strong acid cation ionexchange resin in the hydrogen form, and thereafter into contact with ananion ion exchange resin in the hydroxide form; withdrawing a purifiedsugar solution from the ion exchange stage; concentrating the purifiedsugar solution, to produce a syrup; subjecting the syrup to primarycrystallization in at least one primary crystallization stage, toproduce refined white sugar and primary mother liquor or molasses;subjecting the primary mother liquor to secondary crystallization in atleast one secondary crystallization stage, to produce impurecrystallized sugar and secondary mother liquor or white strap molasses.2. A process according to claim 1, wherein the Impure juice that issubjected to the microfiltration/ultrafiltration is at a temperature ofat least 90° C., with the microfiltration/ultrafiltration comprisingpassing the impure juice through a membrane In the size range 15000Dalton to 300000 Dalton or 200 Angstrom to 0.2 micron, and wherein theclarified sugar juice is cooled to a temperature below 60° C. before itenters the ion exchange stage.
 3. A process according to claim 2, whichincludes concentrating the impure sugar juice, before it enters theclarification stage, to a sugar or sucrose concentration of at least 20%(m/m).
 4. A process according to claim 2, wherein the clarified sugarjuice is cooled to a temperature below 30° C. before It enters the ionexchange stage, or while it passes through the ion exchange stage.
 5. Aprocess according to claim 1, wherein the ion exchange stage comprises asimulated moving bed arrangement or system.
 6. A process according toclaim 1, which includes subjecting the clarified sugar juice to a firstpass through the ion exchange stage, to obtain a partially purifiedsugar solution, and thereafter subjecting the partially purified sugarsolution to at least one further pass through the ion exchange stage, toobtain the purified sugar solution.
 7. A process according to claim 6,which includes regenerating the resins from time to time by contactingthe strong acid cation resin with a strong acid, with an acid streamrich in potassium salts thereby being obtained, and contacting the anionresin with a strong or weak base, with an alkaline stream with is richin nitrogen thereby being obtained.
 8. A process according to claim 6,wherein the concentration of the purified sugar solution into the syrupis effected by means of evaporation, with the resultant syrup having asucrose or sugar concentration of about 65% (m/m).
 9. A processaccording to claim 6, which includes subjecting the purified sugarsolution from the ion exchange stage, or the partially purified sugarsolution of the ion exchange stage, to further decolourizing in adecolourizing stage.
 10. A process according to claim 9, wherein thedecolourizing stage includes an anion resin In the chloride form, withthe partially purified sugar solution, after the first pass thereofthrough the ion exchange stage, being brought into contact with theanion resin in the chloride form in the further ion exchange stage, andthereafter being subjected to the second pass through the ion exchangestage.
 11. A process according to claim 9, wherein the decolourizingstage includes an anion resin in the hydroxide form, an absorptionresin, activated carbon, or another absorption medium, with the purifiedsugar solution from the ion exchange stage being brought into contactwith the anion resin, the absorption resin, the activated carbon or theother absorption medium.
 12. A process according to claim 10, whereinthe primary crystallization is effected in a plurality of sequentialstages or boilings, with the secondary crystallization also beingeffected in a plurality of sequential stages or boilings, and with theImpure crystallized sugar from all the secondary crystallization stagesor boilings being remelted or redissolved and recycled to the syrupahead of the primary crystallization stage.
 13. A process according toclaim 6, which includes subjecting the syrup, prior to the primarycrystallization, to decolourizing crystallization in a decolourizingcrystallization stage, to produce low colour white sugar and tertiarymolasses; remelting or redissolving the low colour white sugar toproduce a remelted sugar solution which is then subjected to the primarycrystallization in the primary crystallization stage; returning theprimary mother liquor or molasses produced in the primarycrystallization stage to the decolourizing crystallization stage;subjecting the tertiary molasses from the decolourizing crystallizationstage to mill crystallization in a mill crystallization stage to producethe white strap molasses and impure crystallized white sugar; andreturning the impure crystallized white sugar to the decolourizingcrystallization stage, with the decolouring crystallization and the millcrystallization constituting the secondary crystallization.
 14. Aprocess for treating impure cane derived sugar juice, which processcomprises subjecting, in a clarification stage, impure cane derivedsugar juice to microfiltration/ultrafiltration to decrease the levels ofsuspended solids, organic non sugar impurities and/or colour therein;sequentially passing the resultant clarified sugar juice through atleast one ion exchange stage by bringing the clarified sugar juice intocontact with a strong acid cation ion exchange resin in the hydrogenform, and thereafter into contact with an anion ion exchange resin inthe hydroxide form; withdrawing a purified sugar solution from the ionexchange stage; subjecting the purified sugar solution from the ionexchange stage to further decolourizing in a decolourizing stage, toobtain a decolourized purified sugar solution; concentrating thepurified sugar solution, to produce a syrup; subjecting the syrup toprimary crystallization in at least one primary crystallization stage,to produce refined white sugar and primary mother liquor or molasses;subjecting the primary mother liquor to secondary crystallization in atleast one secondary crystallization stage, to produce impurecrystallized sugar and secondary mother liquor or white strap molasses.15. A process for treating impure cane derived sugar juice, whichprocess comprises: subjecting, in a clarification stage, impure canederived sugar juice to microfiltration/ultrafiltration to decrease thelevels of suspended solids, organic non sugar impurities and/or colourtherein; sequentially passing the resultant clarified sugar juicethrough an ion exchange stage comprising a simulated moving bed ionexchange system wherein the clarified sugar juice is brought intocontact with a strong acid cation ion exchange resin in the hydrogenform, and thereafter into contact with an anion ion exchange resin inthe hydroxide form; cooling the clarified sugar juice to a temperaturebelow 30° C. before it enters the ion exchange stage, or while it passesthrough the ion exchange stage; withdrawing a purified sugar solutionfrom the ion exchange stage; concentrating the purified sugar solution,to produce a syrup; subjecting the syrup to primary crystallization inat least one primary crystallization stage, to produce refined whitesugar and primary mother liquor or molasses; subjecting the primarymother liquor to secondary crystallization in at least one secondarycrystallization stage, to produce impure crystallized sugar andsecondary mother liquor or white strap molasses.